Signal generator



3 T1@ 5. m. LOUGHLHN SIGNAL GENERATOR Filed June 7, 1947 2 Sheets-Sheetl 10 L WAVE-SIGNAL oRECEIVER.

FIELD- O SCANNING o suemu. GENERATOR LINE- SCANNING J SIGNAL GENERATORINVENTOR. BERNARD D. LOUGHLIN 4 ATTORNEY Lil ,49,93

D. LOUGHLIN SIGNAL GENERATOR R H 3 m & J

2 Shees-Sheet 2 E o o 3 239 .0 .2 2 8:0 5:00 a 250 2.95

INVENTOR. BERNARD D. LOUGHLIN ATTORNEY for one reason or another.

Patented Jan. 31, 1956 SIGNAL GENERATOR Bernard D. Loughlin, Lynbrook,N. Y., assignor to Hazeltine Research, In

ration of Illinois 0., Chicago, 111., a corpo- Application June 7, 1947,Serial No. 753,233

The present invention relates to signal gen- 'erators and, particularly,to such generators of "the so-called blocking-oscillator type forgenerating a signal of repeated-pulse wave form. -While the invention isof general application, it is particularly suited for use in connectionwith the generation of scanning currents or voltages of a televisionreceiver and will be described in that connection.

It is frequently desirable to provide a signal generator having anoperating frequency highly stabilized against variations of operatingcondi tions to which the generator is normally subjected in operation,for example, against variations of oscillator tube characteristics orvariations of the values of one or more energizing potentials or circuitcomponents. An illustrative application is in a television receiverwhich includes an automatic-phase-controlled synchronizing sys-- temwherein the field-scannin and line-scanning generators thereof haveindividual operating frequencies but are controlled to have a phasesynchronized with field-synchronizing and linesynchronizing pulsecomponents of a received television signal. The best and most desirablephase-control action is effected when the phasecontrol system is able totake control and maintain phase synchronization of a controlled scanninggenerator only over a rather limited range of phase deviations fromsynchronism. Therefore, as long as these generators have a naturaloperating frequency quite near the desired fieldscanning andline-scanning frequencies, it is not difiicult for the phase-controlsystem to maintain the desired synchronization of their operation. Inpractice, however, these scanning signal generators heretofore proposeddo not usual- -ly exhibit unduly high frequency stability. This isparticularly true during periods of warm-up immediately following themoment when the television receiver is placed in operation or duringperiods when the energization of the generator may experiencesubstantial fluctuations in value Frequency instability may result incomplete loss of phase control or may cause a rather sluggish anddisagreeable control action requiring an appreciable interval for thephase-controlled synchronization to be effected.

It is an object of the present invention, there- :fore, to provide a newand improved signal generator which avoids one or more of thelimitations and disadvantages of prior such generators.

It is a further object of the invention to provide 14 Claims. (Cl.250-36) a new and improved signal generator characterized by anexceptionally high frequency stability and one particularly suitable forphase-controlled operation.

It is an additional object of the invention to provide a new andimproved signal generator, adapted to generate a signal ofrepeated-pulse wave form, which possesses stable operatingcharacteristics over a wide range of variations of operation conditionsto which the generator is normally subjected in operation.

It is a further object of the invention to provide a signal generator ofsimplified, inexpensive, and improved circuit arrangement involving aminimum of circuit components.

In accordance with a particular form of the invention, a signalgenerator comprises an oscillatory system for generating oscillations,the system including an energizing circuit in which the energizingcurrent thereof is eifectively of repeated-pulse wave form, and meansfor maintainin substantially constant the durations of the pulses of theenergizin current and for limiting the amplitudes thereof. The generatorincludes means responsive to the unidirectional component of theenergizing current yet having much less response to thepulse-periodicity component thereof for controlling the oscillatorysystem to maintain a controlled relationship between the average valueof the energizing current and the average valu of the energizingpotential of the energizing circuit, thereby to maintain substantiallyconstant the periodicity of the generated oscillations.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, anditsscope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a circuit diagram, partlyschematic, representing a complete television receiver which includessignal generators embodying the present invention in a particular form;and Fig. 2 graphically represents certain operating characteristics ofthe generator of the invention and is used as an aid in explaining itsoperation.

Referring now more particularly to Fig. 1 of the drawings, thetelevision receiver includes a wave-signal receiver 10 having an inputcircuit coupled to an antenna system II. It will be understood that theunit it includes in conventional manner one or more stages ofwave-signal amplification, an oscillator-modulator and one or morestages of intermediate-frequency amplification if desired, a wave-signaldetector for deriving the image-modulation components of a receivedtelevision signal, means for deriving and separating thesynchronizing-signal components of the television signal, and one ormore stages of video amplification for amplifying the derivedimage-modulation components. The video output circuit of the unit Iii iscoupled in conventional manner to an intensity-control electrode of acathode-ray type of image reproducer l2. The television receiver alsoincludes a field-scanning phase-control system l3 and a line-scanningphase-control system l4 each of which is shown by way of example as ofthe type disclosed and claimed in the United States Reissue Patent No.22,655 granted March 24, 1942 to Pierre Marie Gabriel. Toulon, entitledSynchronization system for television, andassigned to the'same assigneeas the present application. The arrangement of the phase-control systemI3 is shown as it appears in the Toulon patent and includes an inputcircuit coupled to the output circuit of the field synchronizing-signalseparator arrangement of the unit ll] and a unidirectional controlsignaloutput circuit coupled to a signal generator l more fully describedhereinafter. The output circuit of the latter unit is coupled to acontrol circuit of a field-scanning signal generator 56 which may be ofany conventional type having an operation synchronized by asynchronizing signal of pulse wave form applied thereto. The outputcircuit of the generator 16 is coupled to the vertical-deflectingelectrodes V of the reproducing tube l2. The phase-control system [4likewise has an input circuit coupled to the output circuit of the linesynchronizing-signal separator arrangement of the unit and has acontrol-signal output circuit coupled to a signal generator l5a, whichis essentially similar to the signal generator l5 and will be describedmore fully hereinafter. The output circuit of the generator lfia iscoupled to a control circuit of a linescanning signal generator ll, theoutput circuit of which is coupled to the horizontal-deflectingelectrodes H of the reproducing tube I2. As required in theaforementioned Toulon synchronization system, an output circuit of thesignal generator it is coupled to another input circuit of thephase-control system l3 and an output circuit of the signal generator I!is similarly coupled to another input circuit of the phasecontrol systemi i.

It will be understood that the various units just described may,with-the exception of the signal generators l5 and Ms, be of aconventional'construction and operation the details of which are wellknown in the art, rendering detailed description thereof unnecessary.Considering briefly the operation of the television receiver as a whole,and neglecting for the moment the operation of the signal generators l5and We presently to be described, a desired image-modulated wave signalis received and amplified by the wavesignal receiver ii and theimage-signal and synchronizing-signal modulation components are derivedby the detector thereof. The image components are, in turn, amplified inthe video amplifier of the unit IB and are applied to theintensity-control electrode of the image reproducer !2 to modulate thecathode-ray beam thereof. The synchronizing signal components derived bythe detector of the unit I!) are separated from the image-signalcomponents, and the field-synchronizing and line-synchronizing signalsare separated from each other and applied to the respectivephase-control systems l3 and I l. The detailed operation of the units 13and I4 is fully explained in the aforementioned Toulon patent and willnot be repeated here. Sufiice it to say that each of these unitsdevelops an output unidirectional signal having a value varying withdeviations of phase of the scanning signal relative to thesynchronizing-signal components applied thereto. The output signal ofthe phasecontrol system l3 controls the phase of the oscillationsgenerated by the signal generator I5 which in turn controls the phase ofthe fieldscanning signal generated by the generator [6. The outputsignal of the phase-control system [4 similarly controls the phase ofthe oscillations generated by the signal generator it.. which in turncontrols the phase of the line-scanning signal generated by thegenerator H, The fieldscanning generator It generates and applies ascanning signal of saw-tooth wave form to the field-scanning electrode Vof the image reproducer l2 while the line-scanning generator I! appliesa scanning signal of saw-tooth wave form to the line-scanning electrodesI-I thereof, thereby to deflect the cathode-ray beam of the imagereproducer I! in two directions normal to each other visually toreproduce the received television image.

Referring now more particularly to the portion of the receiver embodyingthe present invention, the signal generator I5 comprises an oscillatorysystem for generating oscillations. This system includes acontrollable-transconductance vacr uum tube l8 having input electrodesincluded in an input circuit and output electrodes included in anenergizing circuit regeneratively coupled to the input circuit. Inparticular, the tube l8 includes a control electrode l9 and a cathode 20coupled to an input circuit comprising a first winding 2! of atransformer 22, and includes an anode 23 coupled with the cathode 29 inan energizing circuit comprising a second transformer winding 24regeneratively coupled to the winding 2|. The winding 2| is tuned by acondenser C to a frequency much higher than the frequency of theoscillations generated by the generator I5.

The energizing current of the vacuum tube I8 is of repeated-pulse wave.form and the generator [5 includes means for maintaining substantiallyconstant the durations of the pulses of the energizing current and forlimiting the amplitudes thereof. Thev portion of this means whicheifects limiting of the amplitudes of the pulses of the energizingcurrent comprises a resistor 25 serially included in the energizingcircuit of the vacuum tube l8 and having a value of resistance muchlarger than the remaining impedance of the energizing circuit during apulse of the energizing current. In particular, the. resistor 25 isserially included between the transformer winding 24 and a source-ofenergizing potential, indicated as +3. The other portion of the meanslast mentioned, namely that for maintaining substantially constant thedurations of the pulses of the energizing current, comprises meansresponsive to the initiation of each pulse of the current forterminating each pulse after a predetermined fixed time interval. Inparticular, this, means comprises a delay network 26, open circuited atits remote end and having a predetermined fixed time delay establishingthe energizing-current pulse duration, coupled between the low-potentialterminal of the transformer winding 2-! and ground.

I The. signal: generator I also includes means responsive to" theunidirectional component of the energizing current .yet having much lessresponse to the pulse-periodicity component thereof for controlling theoscillatory system to maintain a controlled relationship between theaverage value of the e'nerg'izing current and the average value of theenergizing potential+B of the energi ing circuit, thereby to maintainsubstantially constant the periodicity of the oscillations generated bythe signal generator I5. This means comprises a time-constant orresistivecapa'citive network comprising a resistor 21 andparallel-connected condenser 28 included in the jcathodl-zflcircuit ofthe vacuum tube I8. As thus arranged, 'th'e'network 21, 28degeneratively couples the input and energizing circuits of theoscillatory system with respect to the unidirectional component of theenergizing current yet providing no appreciable coupling between thecircuits with respect to the pulse-periodicity component thereof. Thetime-constant network 21, 28'iri'particular has a time constant shortwith relation to undesired variations of the unidirectional component ofthe energizing current yet long with relation to the pulse-periodicitycomponent thereof. It is effective to derive a control effect orunidirectional control bias which is so applied to the input circuit ofthe oscillatory system as to control the transconcluctance of'the vacuumtube I8 to maintain a desired substantially constant relationshipbetweenthe average Value of energizing current and the average value ofenergizing potential.

The control bias developed across the net- .work 21;: 28 from theaverage value of the energizing current is much larger than. thatrequired in the input circuit of the oscillatory system to bias thevacuum tube I8 to anode-current "cutoff. The-generator I5- also includesmeans responsive to the energizing potential +B of he energizing circuitfor applying to the input c ir'c'uit a bia's potential having a value toprovide with thebias developed across the network 21, -28 a normaloperating bias for the input circuit yet-a=res'ultant bias which varieswith the value of the energizing potential +13. This means comprises apotential divider having a first resistor 29 and asecoridresistor 30coupled in .series across the source of energizing potential J-J- B.with the junction 01' the resistors 29 and 30 'jjcoupled through aresistor 3| and through the transformer winding 2i to the controlelectrode :IQ of the vacuum tube I8.

Thegenera'tor I5 also includes means for adjus i'ng the value of thebias provided by the 'fmeans last described to vary the relationshipbetween the energizing current and the energizing lpotential', therebyto" adjust to a desired value "the periodicity of the generatedoscillations. This means comprises a vacuum tube 32 having a controlelectrode 33 and-cathode 34 coupled to the output circuit of'thephase-control system I3 and. having an" anode 35 coupled with thecathode 34faci'oss the resistor 39 of the potential dividen f f'ffConsidering now the operation of the signal j'generator just described,and'referring to the curves of 'Fig. 2, it will be assumed at the outsetthat'thej oscillatory system at time to is at a point in' its "operatingcycle where the energizing or "the anode current of thevacuum tube I8has just ceased to flow. The potential of the point P at the junction ofthe resistor 3I, the delay network 26, and the transformer winding 2Ihas at C thereupon increases 'withitime and at time n has such value asto cause the control electrode I9 of tube I8 to ,become conductiveduring thepositive .the point P of the oscillatory discharge pulse whichtravels down the delay network 26 toward its remote end. At the sametime the conductive condition of the control electrode reduces theconductance of the tuned by curve D, -tions developed in the latter nolonger increases but remains at a substantially uniform amplitude levellevel.

.lations in the tuned circuit 2|, C are tube I8 slowly increases invalue, as

the'time to a relatively low value and thereafter increases in value asthe network 26 charges exponentially through the resistor 3| toward thevalue of positive potential E30 developed across the voltage dividerresistor 3|]. The manner of potential variation of this point isrepresented by curve A. It is assumed that previous cycles of operationof the oscillatory system have caused a value of potential EK to bedeveloped across the cathode resistor 27 and condenser 28 from theaverage value of anode current of the vac uum tube I8. The broken-linecurve B of Fig. 2 represents the cutoff bias E0 of the vacuum tube I8;that is, the bias applied to the control electrode I9 of the vacuum tubeI8 and of value sufficiently less than the cathode bias Ex that theanode current of the tube I8 just ceases to flow. It is apparent thatthe resultant bias applied at any given time between the controlelectrode I9 and cathode 20 of tube I8 is the difference between thevalues of curve A and of the relatively constant value of cathode biasEK. Therefore, when the potential at the point P becomes larger than thecutoff bias Eo at time t1, anode current is initiated in the vacuum tubeIt. During the interval to-tr when the vacuum tube I8 is biased tocutoff, the resonant circuit comprising the transformer winding 2I andcondenser C has a positive value of conductance as represented by thesolid-line curve D, and high-frequency oscillations previously developedin the resonant circuit prior to time to die away exponentially inamplitude during interval to-t1, as represented by solid-line curve E.

As soon as anode current begins to flow in the vacuum tube I8 at timet1, the regenerative coupling between the transformer windings 2| and 24causes the input electrodes of the vacuum tube I8 to reduce the positiveconductance of the resonant circuit 2 I, C in well-known manner andeventually causes this circuit to have a resultant negative conductance,as indicated by curve D. The amplitude of the high-frequencyoscillations developed in the resonant circuit 2|, in an exponentialmanner relative to its cathode 20 peak portion of each oscillation. Thecontrol electrode I9 upon becoming conductive immediately reduces thepotential at system to initiate a circuit 2|, C substantially to zero,as indicated so that the amplitude of the oscillacommonly called thesaturation During the interval iii-4E2 when the oscilbuilding up to thesaturation level, the anode current of the represented by curve F, butquickly increases at time 132 to a .maximum value limited by the highvalue of 'resistanceof the resistor 25. The dischage pulse previouslymentioned travels down the delay network 26 to its remote end where itis reflected without reversal of polarity and at time is arrives back atthe input terminals of the network. The potential at the point Pthereupon suddenly drops to the value which it had at the time to creaseof the average value of 'an'od'e in dropping causes the controlelectrode 19 to bias the vacuum tube Hi again to :anodecurrent cutoff.This terminates one cycle of operation of the oscillatory system andinitiates a new cycle of the operation described.

In the operation of the oscillatory system, it is desirable that theoscillations developed in the resonant circuit 2|, C hang over from oneoperating cycle of the system to the next. That is, the amplitude of'thedeveloped oscillations preferably should not decrease to zero during theinterval to-tr, but rather should have an amplitude value at time 151much larger than any noise disturbances which may exist in theoscillatory system. This ensures that the oscillatory build- :upinterval t1-t2 shall remain uniform from one cycle to the next, therebyto avoid slight variations in the'value of this interval which otherwisewould occur if the oscillations of the circuit 21,

C had initial amplitudes varying :in random fashion with the amplitudeof transient noise disturbances. As is well known, oscillationsdeveloped in the resonant circuit 2|, C have increasing hang-overamplitudes with increasing values of shunt circuit resistance and,hence, the hang-over characteristics may be controlled as desired bycontrol of the high-frequency re sistance of the inductor 2! andcondenserC.

Assume now that the transconductance of the vacuum tube l8 suddenlyincreases for one reason or another. Upon the vacuum tube 18 becomingconductive at time t1, its increased transconductance causes the tunedcircuit 2|, C to have a conductance changing more .rapidl-ywith time, asrepresented by broken-line curve vD, so that r the amplitude of theoscillations developed in the circuit also increases more rapidly withtime, as represented by the broken-line curve E... The saturation levelof the developed oscillations is reached more quickly at time t2 so thatthe anode current now has a wave form as represented by'broken-linecurve F. The duration of each anode pulse has the same value 't2't3' asin the condition first assumed since the pulse duration is controlled bythe time delay of the network. Thus by virtue of the assumed increase ofthe transconductance of the 'vacuum'tube T8, the oscillatory period ofthe oscillatory system is decreased by the time interval t3-*ta so thatthe,

frequency of the generated oscillations of the system increases. This,of course, effects an incurrent of "theva cuurn tube 18 since therearenow a'larger mumberofanode-current pulses perunit of time.

The increased value of averageanode current 'increases "the average'bias potential developed across the cathode resistor 21 and condenser28.

The larger value of this bias potential, however,

is effective to reduce the transconductance of the vacuum tube 13substantially to "the "value which it had under the condition firstassumed. When the transconductance is thus reduced, the oscillatorysystem has substantially the 1 operation described with relation to thefirstaassumed con- :ditionand represented '-'by curves D, E and F of i.Fig. 2. Thus, the degenerative "action of the cathode elements 27, 28'is effective to maintain the frequency of oscillation of theoscillatory system substantially constant with variations of thetransconductance of the vacuum tube 18.

The zfollowing mathematical analysis of the oscillatory-system operationwill render more clear the reason for its :high operating stability.

It is apparent that the mormal operating bias 'jEKi'g "between thecontrol electrodeand cathode;

of-the tube [8 during the oscillatory build-'up interval 'tl-t2 is:given by the relation EK-g=EK--Ed (1"),

where Eg KIEB ('2) (K1 is an arbitray constant related to the values ofthe resistors Hand 30) EB- 'the value of the energizing potential :FB

EK: RK

p R n where R=the value of resistance of the resistor 25 The averagevalue of anode current vi w-of thertuhe itlmay be eXpr-essedbytherelation 4 where te the pulse duration of the anode-current pulses asestablished by the delay network 2 6 tr the oscillatoryperiod of theoscillatory system Tie-arranging Equation 5:

-Now if Equations'e and '7 are combined and re- .membering that thequantity .-EK--K is .=.much smaller than either the control electroderbias Eg or the cathode potential :EK, :it can Joe shown that theoscillatory period of the oscillatory system has the-following value I.T f a i8) In Equation 8, the pulse duration ta is constant andestablished by the delay of the delay network '26. The fraction K1 ofthe potential +113 applied by the voltage divider 29, 3D to the controlelectrode 19 of tube 181s also'cons'tantas ialsoristhe .valutRx of thecathode resistor-'2] and the value R of the resistor 25. .It isconsequently apparent that the oscillatory system has high frequencystab'ility since its oscillatory period is established almost entirel bycircuit elements of constant value. 7 Referring now to Equation Eg-theanode-current pulse duration is esta'blished'by the rdelaylne'twor' kflfi'has constant value and it will beapparentthat the oscillatoryperiod 11' of the system is maintained constant with variations ofoperatingconditions of the system if the average value iav jfvaries inthesame sense andproportionately with variationsof the peak value z'of'anode current of the tube 18. From Equations 2 and i3, assumanodecurrent of tube It will be apparent from the latter equation and fromEquation4 that a selection of the value 'of the constant K1 may be madewhich will maintain this desired relation between the average and thepeak values of anode current with variations of the energizing potential+B. When this is done, the oscillatory system has good frequencystability for Variations of the energizing potential +B as well as forvariations of transconductance of tube l8 as earlier described.

1 It is apparent from the foregoing described operation of theoscillatory system that it possesses good frequency stability againstvariations of the usual operating conditions to which the system isnormally subjected in operation. It is further apparent that thetransconductance of the vacuum tube I 8 controls the oscillatory periodof the system in the absence of the stabilizing action of the cathoderesistor 21 and condenser 28, but that the degenerative effect of thelatter elements so controls the transconductance of the tube l8 bcontrol of its average current and in such a direction as to degeneratethe eifect of variations of transconductance of this tube. For thispurpose, and as indicated more particularly in Fig. 2, the value of theresistor 21 is preferably selected so large that the value of cathodepotential Ex developed from the average value of the anode current ofthe tube I8 is very much larger than the cutoif bias of this tube.

The phase-control tube 32 is responsive to the unidirectionalphase-control signal developed in the output circuit of thephase-control system 13 to vary the impedance between its anode 35 andcathode 34. Since the latter impedance is in parallel with the resistor30 of the potential divider 29, 33, variations of anode-cathodeimpedance of the tube 32 are effective to vary the value of the positivebias potential applied from the potential divider to the controlelectrode IQ of the tube l8. Reference to Equation 8 above shows thatthe phase-control tube 32 in varying the quantity K1 is effective tovary the oscillatory period of the oscillatory system. The oscillationsgenerated by the generator l are applied to the field-scanning generatorl6 and are efiective to synchronize the operation of the latter. Thesignal generated by the generator i6 is applied to the phase-controlsystem 13 to develop in the output circuit of the latter a phase-controlsignal whenever the phase of the signal of the generator I6 departs fromsynchronization with the fieldsignal applied from thereceiver H] It willtherefore be apparent that the operation of the phase-control tube 32 inits control over the periodicity of the generator i5 is eficctive tomaintain the desired phase synchronization between the output signal ofthe generator I 6 and the field-synchronizing signal of a receivedtelevision signal.

The generator la. is essentially similar to the generator l5 andincludes similar circuit elements, identified similar reference numeralsa, except that the periodicity generated by the generator 35s is that ofthe much higher frequency line-scanning signal. By way of illustratingthe several difi'erent manners in which the periodicity of a cathoderesistor 21a. The phase-control signal developed in the output circuitof the phasecontrol system H thus is efiective to vary the efiectiveresistance in the cathode circuit of the tube l8e. This is a variationof the quantit R1: of Equation 8 from which it will be apparent that thephase-control tube 32a again is eflective to vary the periodicity of thegenerator Mia. The operation of the generator l5a is otherwiseessentially similar to that of the generator I 5 and will not berepeated.

From the above description of the invention, it will be apparent that a.signal generator embodying the invention has the advantages that it ischaracterized in operation by exceptionally good frequency stability andis one particularly suitable for a phase-controlled operation as in ascanning system of a television receiver. The generator of the :presentinvention has the additional advantages that it possesses very stableoperating characteristics over a wide range of variations of operatingconditions to which the generator is normally subjected in operation,yet is of simple and inexpensive arrangement involving a minimum ofcircuit components.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an energizing circuit in which theenergizing current thereof is effectively of repeatedpulse wave form,means for maintaining substantially constant the durations of the pulsesof said current and for limiting the amplitudes thereof, and meansresponsive to the unidirectional component of said current yet havingmuch 1685 response to the pulse-periodicity component thereof forcontrolling said oscillatory-system periodicity by maintaining acontrolled relationship between the average value of said current andthe average value of energizing potential of said energizing circuit,thereby to maintain substantially constant the average periodicity ofsaid generated oscillations.

2. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an energizing circuit in which theenergizing current thereof is efiectively of repeatedpulse wave form,means for maintaining substantially constant the durations of the pulsesof said current and for limiting the amplitudes thereof, and atime-constant network responsive to said current and having a timeconstant short with relation to undesired variations of theunidirectional component thereof yet long with relation 0 thepulse-periodicity component thereof for controlling said oscillatorysystem to maintain a controlled relationship between the average valueof said current and the average value of energizing potential of saidenergizing circuit, thereby to maintain substantially constant theperiodicity of said generated oscillations. i

3. A signal generator comprising, an oscillatory system for generatingoscillations, said system including a controllable-transconductancevacuum tube and an energizing circuit therefor in which the energizingcurrent thereof is effectively of repeated-pulse wave form, means formaintaining substantiall constant the durations of the accuses pulses ofsaid current and for limiting the amplitudes thereof, and meansresponsive to the unidirectional component of said current yet havingless response to the pulse-periodicity component thereof for deriving acontrol bias effective to control the transconductance of said tube tomaintain a controlled relationship between the average value or saidcurrent and the average value of energizing potential of said energizingcircuit, thereby to maintain substantially constantthe periodicity ofsaid generated oscillations.

' 4. A signal generator comprising, an oscillatory system for generatingoscillations, said system ineluding an energizing circuit in which theenerg'lzing current thereof is effectively of repeatedpulse wave form,means for maintaining substantially constant the durations of the pulsesof said current and for limiting the amplitudes thereof, meansresponsive to the unidirectional component of said current yet havingmuch less response to the pulse-periodicity component thereof forcontrolling said oscillatory system to maintain a controlledrelationship between the average value of said current and the averagevalue of energizing potential of said energizing circuit, thereby tomaintain substantially con stant the periodicity of said generatedoscillations, and means for adjusting said currentpotential relationshipto adjust to a desired value the periodicity of said generatedoscillations.

5. A signal generator comprising, oscillatory system for generatingoscillations, said system including a co-ntrollablfe-transconductancevacuum tube and an energizing circuit therefor in which the energizingcurrent thereof is efiectively of repeated-pulse wave form, means formain taining substantially constant the durations of the pulses of saidcurrent and for limiting the amplitudes thereof, means responsive to theunidirectional component of said current yet having much less responseto the pulse-periodicity component thereof'for deriving a control biaseffective to control the transconductance of said tube to maintain acontrolled relationship between the average value of said current andthe average value of energizing potential of said energizing circuit,thereby to maintain substantiall constant the periodicity of saidgenerated oscillations, and means for adjusting the value of a secondbias of said tube to vary said currentpotential relationship to adjustto a desired value the perio i'eity of said generated oscillations.

6; A signal generator comprising, a regenerative system having input andoutput circuits regeneratively coupled to generate oscillations, theoutput-circuit current of said system being effectively ofrepeated-pulse wave form, means for maintaining substantially constantthe durations of the pulses of said current and for limiting theamplitudes thereof, and means responsive to the unidirectionalcomponent. of said current yet having much less response to thepulse-periodicity component thereof for controlling said oscillatorysystem to maintain a controlled relationship between the average valueof said current and the average value of energizing potential of saidenergizing circuit, thereby to maintain substantially constant theperiodicity of said generated oscillations.

'7. A signal generator comprising, an oscillatory system for generatingoscillations, said system ineluding an input circuit and an energizingcircuit in which the energizing current thereof is eiiectively ofrepeated-pulsewave form, means for maintaining substantially constantthe durations of thepulses of said current and for limiting theamplitudes. thereof, and: means common to said circuits and responsiveto the unidirectional component of said current yet having much lessresponse to the pulse-periodicity component thereof for deriving acontrol effect and for applying said control effect to said inputcircuit to maintain a controlled relationship between the average valueof said current and the average value of energizing potential of said.energizing circuit, thereby to maintain substantially constant theperiodicity of said generated oscillations.

8. A signal generator comprising, an oscillatory system. for generatingoscillations, said system including an input'circuit and an energizingcircuit in which the energizing current thereof'is ellfectively ofrepeated-pulse wave form, means for ma ntaining substantially constantthe durations of the pulses of said current and for limiting theamplitudes thereof, and means common to said circuits and responsivesubstantially only to the unidirectional component of said current forderiving a unidirectional control potential for applying said potentialto said input circuit to maintain a controlled relationship betweentheaverage value of said current and the average value of energizingpotential of said energizing circuit, thereby to maintain substantiallyconstant the periodicity of said generated oscillations.

9. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an input circuit and an energizingcircuit in which the energizing current thereof is effectively ofrepeated-pulse wave form, means for maintaining substantially constantthe durations of the pulses of said current and for limiting theamplitudes thereof, and a resistor and parallelconnected condensercommon to said circuits for degeneratively coupling said circuits withrespect to the unidirectional component of said current yet providing noappreciable coupling'between said circuits with respect to thepulseperiodicity component of said current for controlling saidoscillatory system to maintain a controlled relationship between theaverage value of said current and the average value of energizingpotential of said energizing circuit, thereby to maintain substantiallyconstant the periodicity of said generated oscillations.

10. A signal generator comprising, an oscillatory system including avacuum tube having input electrodes included in an input circuit andoutput electrodes included in an energizing circuit regeneratively'coupled to said input circuit to generate oscillations, the energizingcurrent of said energizing circuit being effectively of repeated pulsewave form, means for maintaining substantially constant the durations ofthe pulses of said current and for limiting the amplitudes thereof, aresistive-capacitive network common to said circuits and responsive tothe unidirectional component of said current yet having much lessresponse to the pulse-periodicity component thereof for developing fromthe average value of said current a bias potential for. said inputcircuit much larger than that requiredv therein to bias said tube toanode-current cutoff, and means responsive to the energizing potentialof said energizing circuit for applying to said input circuit a biaspotential having a, value which provides with said first-mentioned biaspotential 8 normal. operating bias. for said input circuit yet aresultant bias therefor which varies with the value of said energizingpotential, thereby to maintain substantially constant the periodicity01. said generated oscillations.

ll. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an energizing circuit in which theenergizing current thereof is efiectively of repeated-pulse wave form,means for limiting the amplitudes of the pulses of said current, meansfor maintaining substantially constant the :durations of the pulses ofsaid current, and means responsive to the unidirectional component ofsaid current yet having much less response to the pulse-periodicitycomponent thereof for controlling said oscillatory system to maintain acontrolled relationship between the average value of said current andthe average value of energizing potential of said energizing circuit,thereby to maintain substantially constant the periodicity of saidgenerated oscillations.

12. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an energizing circuit in which theenergizing current thereof is effectively of repeated-pulse wave form,means for limiting the amplitudes of the pulses of said current, meansresponsive to the initiation of each pulse of said current forterminating said each pulse after a predetermined fixed time interval tomaintain substantially constant the durations of said current pulses,and means responsive to the unidirectional component of said current yethaving much less response to the pulse-periodicity component thereof forcontrolling said oscillatory system to maintain a controlledrelationship between the average value of said current and the averagevalue of energizing potential of said energizing circuit, thereby tomaintain substantially constant the periodicity of said generatedoscillations.

13. A signal generator comprising, an oscillatory system for generatingoscillations, said system including an energizing circuit in which theenergizing current thereof is effectively of repeated-pulse wave form,means for limiting the amplitudes of the pulses of said current, a delay4 network responsive to the initiation of each pulse of said current forterminating said each pulse after a predetermined fixed time intervalestablished by said network to maintain substantially constant thedurations of said current pulses, and means responsive to theunidirectional component of said current yet having much less responseto the pulse-periodicity component thereof for com trolling saidoscillatory system to maintain a e011- trolled relationship between theaverage value of said current and the average value of energizingpotential of said energizing circuit, thereby to maintain substantiallyconstant the periodicity of said generated oscillations.

14. A signal generator comprising, an oscillatory system including avacuum tube having anode and cathode electrodes coupled to an energizingcircuit and input electrodes coupled to an input circuit for generatingoscillations, said tube in its conductive state having a relatively lowvalue of anode-to-cathode impedance and the energizing current ofenergizing circuit being effectively cf repeated pulse Wave form, aresistive impedance included in said energizing circuit and having avalue of impedance much larger than said anode-cathode impedance forlimiting the amplitudes of the pulses of said current, means formaintaining substantially constant the durations of the pulses of saidcurrent, and means responsive to the unidirectional component of saidcurrent yet having much less response to the pulse-periodicity componentthereof for controlling said oscillatory system to maintain a controlledrelationship between the average value of said current and the averagevalue of energizing potential of said energizing circuit, thereby tomaintain substantially constant the periodicity of said generatedoscillations.

BERNARD D. LOUGHLIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Niunber Name Date 2,165,770 Tolson July 11, 19392,344,810 Fredendall Mar. 21, 1944

